(1) Field of the Invention
The present invention relates to a projecting apparatus which projects an image for display using a discharge lamp as a light source and, more particularly, to a cooling structure of a projecting apparatus suitable for cooling heat sources including a light source unit.
(2) Description of the Related Arts
A projecting apparatus forms an optical image by modulating, according to a video signal, an optical beam received from a light source using a display device, for example, a liquid crystal panel and projects the optical image thus formed on a projection surface such as an external screen or wall surface using a projection lens or projection mirror.
Generally, such a projecting apparatus includes, as a light source, a discharge lamp (lamp bulb), for example, an extra-high pressure mercury lamp or metal halide lamp of a short arc type (for example, with an arc length of up to 1.5 mm) which can be regarded as a point light source containing a high-pressure (about 15 MPa or more) light-emitting gas.
Such a discharge lamp has a rear portion covered with a reflector and a front portion covered with an optically transmissive explosion-proof glass for preventing, in the event of explosion of the discharge lamp, fractions of the discharge lamp from frying off, and makes up a light source unit (also referred to as a lamp unit) having an almost sealed structure. While the discharge lamp is lit, therefore, its temperature rises lowering its reliability and shortening its life. As a means of lowering the temperature of a discharge lamp, forced air cooling made using fans is considered effective. When a projecting apparatus is operated, a portion above the discharge lamp is likely to become the hottest part of the projecting apparatus. Under such circumstances, cooling systems designed to intensively cool a portion above the discharge lamp so as to keep the discharge lamp at appropriate temperature have been proposed.
The appropriate temperature of a discharge lamp depends on the type, manufacturer, and specifications of the discharge lamp. Generally, however, the difference in temperature between portions above and below a discharge lamp is preferred to be smaller with a temperature difference exceeding 150° C. considered unallowable.
Using a discharge lamp which is not kept at an appropriate temperature for extended periods of time shortens the life of the discharge lamp, for example, by causing the discharge lamp to explode or to be disabled before a normal length of its life expires.
Existing projecting apparatuses are generally classified into those of a surface installation type which are horizontally installed on a flat surface, for example, on the top of a desk and those of a suspended installation type which are suspended, for example, from the ceiling. Recent models of projecting apparatuses include many which are convertible between surface installation and suspended installation.
In many cases, a projecting apparatus to be horizontally installed on the top of a desk is set to output a projection beam diagonally upwardly so that the beam can project an image on a projection surface, for example an external screen or wall surface located upwardly forward of the desk. When such a projecting apparatus set to output a projection beam diagonally upwardly is suspended from the ceiling as it is, it is caused to project an image on the ceiling. To enable such a projecting apparatus to downwardly project an image, it is necessary to suspend the projecting apparatus upside down. Installing the projecting apparatus upside down positions the light source unit included in the projecting apparatus also upside down. A projecting apparatus which may be installed upside down as required is required to have a cooling structure in which the discharge lamp included in the projecting apparatus can be kept at an appropriate temperature whether or not the projecting apparatus is installed upside down. Furthermore, whether or not the projecting apparatus is installed upside down, the discharge lamp requires, due to its characteristics, that its optical axis be kept horizontal relative to the ground.
A light source unit for a projecting apparatus in which a discharge lamp is forcedly air-cooled whether or not the projecting apparatus is installed upside down is disclosed in Japanese Patent Application Laid-Open Publication No. 2005-24735. To allow the discharge lamp to be kept at an appropriate temperature even when the projecting apparatus is installed upside down, the light source unit is provided with two cooling air inlets, one in an upper side of a reflection mirror included in the light source unit and the other in a lower side of the reflection mirror. The two cooling air inlets are communicated to corresponding cooling air outlets via a pair of cooling air passages fixedly provided in the housing of the light source unit. The two cooling air inlets are provided with one shutter which moves, by its own weight, toward the upper or lower side of the reflection mirror. Depending on whether the projecting apparatus is installed on a flat surface in a normal position or suspended from the ceiling upside down, the shutter moving automatically by its own weight closes either one of the two cooling air inlets allowing the cooling air to be let out only from the corresponding one of the cooling air outlets provided in the upper and lower sides of the reflection mirror, respectively. Thus, the light source unit is designed to allow the portions above and below the discharge lamp to be cooled under unchanged conditions whether the projecting apparatus is installed on a flat surface or suspended from the ceiling so as to always keep the discharge lamp at an appropriate temperature.
To realize, using the above technique, a projecting apparatus which can extend the life of its light source without reducing the reliability and safety of the light source whether the projecting apparatus is installed on a flat surface or suspended from the ceiling, keeping the discharge lamp (lamp bulb) of the projecting apparatus at an appropriate temperature is important.
Recently, it has been increasingly required that projecting apparatuses can be installed in diversified positions as required according to applications. For example, it is recently required that projecting apparatuses, besides being installable on a flat horizontal surface or suspendable from the ceiling as described above, can also be installed differently to upwardly or downwardly project an image.
When a projecting apparatus is horizontally installed on a flat surface or suspended from the ceiling as described above, it is considered possible to keep the discharge lamp of the projecting apparatus at an appropriate temperature using the cooling system proposed in Japanese Patent Application Laid-Open Publication No. 2005-24735. When the projecting apparatus is installed differently than as described above so as to project an image upwardly or downwardly, the cooling system proposed in Japanese Patent Application Laid-Open Publication No. 2005-24735 cannot keep the discharge lamp at an appropriate temperature, so that the life of the discharge lamp may be shortened detracting from the reliability and safety of the discharge lamp.
The cooling system proposed in Japanese Patent Application Laid-Open Publication No. 2005-24735 requires openings provided in a neck portion of the reflector, but such openings cannot always be provided depending on the specifications of the lamp to be used. Thus, there may be cases where the reflector cannot be shaped as described in Japanese Patent Application Laid-Open Publication No. 2005-24735.
An object of the present invention is to provide, so as to solve the above problems, a projecting apparatus including a light source unit which, having a reflector with no opening in its neck portion, is simply configured and which has a cooling structure capable of keeping a discharge lamp (lamp bulb) at an appropriate temperature to extend the life of the light source whether the projecting apparatus is installed on a flat surface or suspended from the ceiling as described above or installed otherwise for upward or downward projection.